The present invention is in the field of electrophotographic printers and copiers. More specifically this invention relates to the corona charging device used to charge the surface of a photoconductor.
The corona charging device usually contains one or more small diameter (e.g. 0.003 inch diameter) corona wires. It is important that these wires be properly tensioned. Excessive tension can result in wire breakage, whereas insufficient tension can result in wire vibration and subsequent non-uniform charging of the photoconductor. Additionally, corona wires have a finite life and must be replaced in the field.
It is common practice to spring load corona wires to achieve the proper tension. One method used to do this is to crimp lugs onto the ends of the wires, secure one end of the wires, and then insert the lugs on the other end through the hook of an extension spring. Multiple wires may then be tensioned by mounting these springs on a tensioner block and rotating and securing the tensioner block at the desired tension. One drawback of this method is that it is difficult to maintain engagement between the lugs and the springs while rotating and securing the tension block. Another drawback is that because the spring and the corona wire are in direct contact in this method, the spring is at the same voltage as the wire, and there is a risk of arcing by the spring. One further problem with this method is that the force of the spring hooks can impart side loads on the lugs, which in turn can impose undue stress on the wires.
A corona wire tensioning mechanism is desired which would allow individual replacement of the corona wires, which would not impart side loads on the wires, and which would easily maintain engagement between the wire and the tensioning mechanism and yet be isolated from the spring so as to minimize the danger of arcing by the spring.